Heretofore, the wheel bearing apparatus for supporting a wheel of vehicle is used for rotationally supporting a wheel hub for mounting a wheel via a double row rolling bearing and there are those for a driving wheel and for a driven wheel. From reasons of structure, the inner ring rotation type is used for the driving wheel and both the inner ring rotation type and the outer ring rotation type are used for the driven wheel. In general, the wheel bearing apparatus is roughly classified into a first generation type in which a double row angular contact ball bearing is arranged between a knuckle forming a portion of a suspension apparatus and a wheel hub, a second generation type in which a body mounting flange or a wheel mounting flange is directly formed on an outer circumference of an outer member, a third generation type in which one of inner raceway surfaces is directly formed on an outer circumference of the wheel hub, or a fourth generation type in which an inner raceway surface is directly formed respectively on the outer circumferences of the wheel hub and an outer joint member of a constant velocity universal joint.
In these wheel bearing apparatus, it is usually equipped with seals having tough sealability for preventing leakage of grease filled in the inside of the bearing as well as preventing enter of rain water or muddy water into the bearing. It has been proposed various kinds of seals having improved sealability and one example of which is shown in FIG. 4. This sealing apparatus comprises a first seal 50 and a second seal 51 arranged in a bearing space radially outward of the first seal 50. The first seal 50 comprises a metal core 52 and a sealing member 53 integrally adhered to the metal core 52 by vulcanized-adhesion. The metal core 52 is press-formed of steel sheet and comprises a cylindrical fitting part 52a fit into an inner circumference of an outer member 54 and an inner part 52b bent from the fitting part 52a and extending radially inward.
On the other hand, the sealing member 53 is formed of synthetic rubber and comprises a side lip 53a and a dust lip 53b secured on an inner end of the inner part 52b of the metal core 52 and inclining radially outward and slide-contacting with a wall surface 56a of a base 56 of a wheel mounting flange 55 via an axial interference, and a radial lip 53c extending radially inward from a base of the dust lip 53b. The radial lip 53c slide-contacts with an outer surface of the base 56 via a radial interference to prevent grease filled in the bearing from flowing out.
The second seal 51 is mounted in the bearing space outside of the first seal 50 and comprises a metal core 58 and a sealing member 59 integrally adhered to the metal core 58 by vulcanized adhesion. The metal core 58 comprises a cylindrical part 58a press-fit onto an outer circumference 57 of the outer member 54, an upstanding flat part 58b extending radially outward, and a flanged part 58c closely contacted with an end face 54c of the outer member 54. The sealing member 59 comprises a dam part 59b and a side lip 59a integrated with the dam part 59b and inclined toward radially outward. The side lip 59a is arranged so that it lies along an inclined part 56b of the wheel mounting flange 55 and opposes thereto via a predetermined gap to form a labyrinth seal 60. The side lip 59a of the second seal 51 is arranged at a position offset from the side lip 53a of the first seal 50 so that the side lip 59a is at a position axially outer than that of the side lip 53a. That is, a tip end of the side lip 59a is arranged at a position so that it is offset axially outward from a wall surface 56a of the base 56 by a distance L1 (L1>0), and the length L2 of the side lip 59a is set larger 3 times or more than its thickness T1 (L2≥3T1). This makes it possible to prevent muddy water etc. from directly entering into the first seal 50. In addition, when a large quantity of muddy water etc. splash over the side lip 59a of the second seal 51, the side lip 59a would be deformed by the pressing force of the muddy water and slide-contacted against the inclined part 56b of the wheel mounting flange 55 and thus the side lip 59a would form a temporally contacting seal under a heavy travelling condition and effectively improve the sealability.
In addition, a height L3 of the dam part 59b is higher than that of a tapered part 57a of the outer circumference 57 of the outer member 54 and set at 3 mm or more and an angle α of the dam part 59b is set at 90°±15°. This makes it possible to surely prevent rain water or muddy water fallen on the outer member during travel of a vehicle from flowing into a space between the wheel mounting flange 55 and the outer member 54 and then to smoothly discharge the rain water or muddy water downward through an annular space formed by the dam part 59b of the second seal 51 and the tapered part 57a (see, e.g., JP2013-032823A).
It is also known a seal 61 shown in FIG. 5. This seal 61 comprises a metal core 65 mounted between an outer member 62 and a wheel hub 64 integrally formed with a wheel mounting flange 63, and a sealing member 66 having four lips integrally adhered to the metal core 65 by vulcanized adhesion.
The sealing member 66 is formed so that it is inclined toward the wheel mounting flange 63 and comprises two side lips 66a, 66b adapted to be elastically contacted with a side surface 63a of the wheel mounting flange 63, a single radial lip 66c and an outer lip 67 positioned radially outside of the side lip 66a and inclined toward the wheel mounting flange 63. The outer lip 67 comprises a projection part 67a projected toward the wheel mounting flange 63, an inclined part 67b extending radially outward toward the side surface 63a of the wheel mounting flange 63, an upstanding part 67c extending from a tip end of the inclined part 67b substantially in parallel with the side surface 63a of the wheel mounting flange 63. This makes it possible to provide the seal 61 which is able to suppress increase of the rotational torque, superior in sealability and has a long sealing life although it has the outer lip 67 (see, e.g., JP2013-200039 A).
In the seal of the prior art shown in FIG. 4, it is possible to prevent muddy water etc. from directly entering to the first seal 50 and improve the sealability due to a temporal seal which is formed by deformation of the side lip 59a and therefore its slide-contact with the inclined part 56b of the wheel mounting flange 55 caused by pressing force applied onto side lip 59a by a large quantity of muddy water entered on the side lip 59a under a heavy travelling condition. On the contrary, in addition to this slide-contact with the wheel mounting flange 55, since the side lip 53a of the first seal 50 is also slide-contacted with the wall surface 56a of the base 56 of the wheel mounting flange, the seal torque and thus the fuel consumption of a vehicle would be necessarily increased.
Similarly to the seal of FIG. 4, increase of the seal torque could not be denied also in the seal 61 of FIG. 5, since two side lips 66a, 66b are always slide-contacted with the side surface 63a of the wheel mounting flange 63.